Delete data on the internet

This recipe covers how to delete data over the internet using the http package.

This recipe uses the following steps:

  1. Add the http package.
  2. Delete data on the server.
  3. Update the screen.

1. Add the http package

To install the http package, add it to the dependencies section of the pubspec.yaml file. You can find the latest version of the http package on pub.dev.

dependencies:
  http: <latest_version>

Import the http package.

import 'package:http/http.dart' as http;

2. Delete data on the server

This recipe covers how to delete an album from the JSONPlaceholder using the http.delete() method. Note that this requires the id of the album that you want to delete. For this example, use something you already know, for example id = 1.

Future<Response> deleteAlbum(String id) async {
  final http.Response response = await http.delete(
    'https://jsonplaceholder.typicode.com/albums/$id',
    headers: <String, String>{
      'Content-Type': 'application/json; charset=UTF-8',
    },
  );
  
  return response;
}

The http.delete() method returns a Future that contains a Response.

  • Future is a core Dart class for working with async operations. A Future object represents a potential value or error that will be available at some time in the future.
  • The http.Response class contains the data received from a successful http call.
  • The deleteAlbum() method takes an id argument that is needed to identify the data to be deleted from the server.

3. Update the screen

In order to check whether the data has been deleted or not, first fetch the data from the JSONPlaceholder using the http.get() method, and display it in the screen. (See the Fetch Data recipe for a complete example.) You should now have a Delete Data button that, when pressed, calls the deleteAlbum() method.

Column(
  mainAxisAlignment: MainAxisAlignment.center,
  children: <Widget>[
    Text('${snapshot.data?.title ?? 'Deleted'}'),
    RaisedButton(
      child: Text('Delete Data'),
      onPressed: () {
       setState(() {
        _futureAlbum = deleteAlbum(snapshot.data.id.toString());
      });
      },
    ),
  ],
);

Now, when you click on the Delete Data button, the deleteAlbum() method is called and the id you are passing is the id of the data that you retrieved from the internet. This means you are going to delete the same data that you fetched from the internet.

Returning a response from the deleteAlbum() method

Once the delete request has been made, you can return a response from the deleteAlbum() method to notify our screen that the data has been deleted.

Future<Album> deleteAlbum(String id) async {
  final http.Response response = await http.delete(
    'https://jsonplaceholder.typicode.com/albums/$id',
    headers: <String, String>{
      'Content-Type': 'application/json; charset=UTF-8',
    },
  );

  if (response.statusCode == 200) {
    // If the server returned a 200 OK response,
    // then parse the JSON. After deleting,
    // you'll get an empty JSON `{}` response.
    // Don't return `null`, otherwise
    // `snapshot.hasData` will always return false
    // on `FutureBuilder`.
    return Album.fromJson(json.decode(response.body));
  } else {
    throw Exception('Failed to delete album.');
  }
}

FutureBuilder() now rebuilds when it receives a response. Since the response won’t have any data in its body if the request was successful, the Album.fromJson() method creates an instance of the Album object with a default value (null in our case). This behavior can be altered in any way you wish.

That’s all! Now you’ve got a function that deletes the data from the internet.

Complete example

import 'dart:async';
import 'dart:convert';

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;

Future<Album> fetchAlbum() async {
  final response =
      await http.get('https://jsonplaceholder.typicode.com/albums/1');

  if (response.statusCode == 200) {
    // If the server did return a 200 OK response, then parse the JSON.
    return Album.fromJson(json.decode(response.body));
  } else {
    // If the server did not return a 200 OK response, then throw an exception.
    throw Exception('Failed to load album');
  }
}

Future<Album> deleteAlbum(String id) async {
  final http.Response response = await http.delete(
    'https://jsonplaceholder.typicode.com/albums/$id',
    headers: <String, String>{
      'Content-Type': 'application/json; charset=UTF-8',
    },
  );

  if (response.statusCode == 200) {
    // If the server did return a 200 OK response,
    // then parse the JSON. After deleting,
    // you'll get an empty JSON `{}` response.
    // Don't return `null`, otherwise `snapshot.hasData`
    // will always return false on `FutureBuilder`.
    return Album.fromJson(jsonDecode(response.body));
  } else {
    // If the server did not return a "200 OK response",
    // then throw an exception.
    throw Exception('Failed to delete album.');
  }
}

class Album {
  final int id;
  final String title;

  Album({this.id, this.title});

  factory Album.fromJson(Map<String, dynamic> json) {
    return Album(
      id: json['id'],
      title: json['title'],
    );
  }
}

void main() {
  runApp(MyApp());
}

class MyApp extends StatefulWidget {
  MyApp({Key key}) : super(key: key);

  @override
  _MyAppState createState() {
    return _MyAppState();
  }
}

class _MyAppState extends State<MyApp> {
  Future<Album> _futureAlbum;

  @override
  void initState() {
    super.initState();
    _futureAlbum = fetchAlbum();
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Delete Data Example',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: Scaffold(
        appBar: AppBar(
          title: Text('Delete Data Example'),
        ),
        body: Center(
          child: FutureBuilder<Album>(
            future: _futureAlbum,
            builder: (context, snapshot) {
              // If the connection is done,
              // check for response data or an error.
              if (snapshot.connectionState == ConnectionState.done) {
                if (snapshot.hasData) {
                  return Column(
                    mainAxisAlignment: MainAxisAlignment.center,
                    children: <Widget>[
                      Text('${snapshot.data?.title ?? 'Deleted'}'),
                      RaisedButton(
                        child: Text('Delete Data'),
                        onPressed: () {
                          setState(() {
                            _futureAlbum =
                                deleteAlbum(snapshot.data.id.toString());
                          });
                        },
                      ),
                    ],
                  );
                } else if (snapshot.hasError) {
                  return Text("${snapshot.error}");
                }
              }

              // By default, show a loading spinner.
              return CircularProgressIndicator();
            },
          ),
        ),
      ),
    );
  }
}